Fuel cells are electrochemical devices which can convert energy stored in fuels to electrical energy efficiencies. High temperature fuel cells include solid oxide fuel cells (SOFC) and molten carbonate fuel cells. These fuel cells may operate using hydrogen and/or hydrocarbon fuels. There are classes of fuel cells, such as the solid oxide regenerative fuel cells, that also allow reversed operation, such that oxidized fuel can be reduced back to unoxidized fuel using electrical energy as an input.
Reformed natural gas is used as source of H2 fuel for SOFC system. Reformation also produces CO2 that does not take part in fuel cell reaction at anode surface and comes out along with product stream, which is mainly water (as steam), CO, and un-utilized H2. Part of the un-utilized fuel should to be recycled back to the inlet feed stream, and non-reactive CO2 in recycle feed reduces the overall solid oxide fuel cell system efficiency.
Removing CO2 from the anode exhaust stream of SOFC systems using a carbon dioxide separator can improve efficiency. CO2 can be separated from a gas mixture using solvents/sorbents, membranes, or cryogenics. A scrubbing process for CO2 separation uses amine solvents. Pressure swing adsorption and temperature swing adsorption are methods to remove CO2 using solid adsorbents such as zeolites and activated carbon. Cryogenics use sub-zero temperature condition for CO2 separation.
However, CO2 separation via porous and non-porous membranes is simpler than other techniques. Accordingly, there is a need for a CO2 separator that includes an improved CO2 membrane structure.